Art of clarifying liquids



G. E. HENKEL ART OF CLARIFYING LIQUIDS I l 1 I l I k llllllll l l lllll Filed Aug. 8, 1940 Nov. 23, 1943.

ATTORNEYS Patented Nov. 23, 1943 V ART OF onAmFYrNq'LIQUIDs I George Henkel ,Cranford, ,N ."J., assig nor, to r Americancentrifugal Corporation, New York,

N. Y., a corporation of Delaware; f

ApplicationAugust s, 194 Serial r a. l sw ms. (c -e en This invention relates to the art of clarifyin liquids, and is especially useful in connection with the separation ofgreases, fats, colloids, and finely divided solids iro'maqueous liquids, such as the liquid 'eflluent froma centrifuge which is handling sludges, for example sewage sludges.

Although the invention, in its broader aspects, is not limited to the-field of sewage disposal, it

will beherein described with referenc to its' use in that field, because it is of especial advantage in the handling and disposal of the liquids there dealt with. The objects and advantages" of the invention will best be understood after a brief consideration of certain sewage disposal problems, which will now'be referred to by way of illustration (though n0t"by"w.ay of limitation of the broader aspects of the invention).

In the sewage disposalart, according to one of the systems at present in use,'the 'rawsewage is subjected to one or more stages of gravity settling, which results in the collection of sludges ofjfor example, 93.75% aqueous liquids and 6.25% solids greaseaetc. {Such sludge is then centrifuged, by machines which remove the major part of the heavier solids, disposable by incineration or in other ways, and which discharge as an effluent most of the liquid portion of the sludge. This effluent, however, may contain, as'a'n example, about 3.12% of relatively fine solidsjfats, greases, etc. In such a system, it is quite a problem to dispose of the effluent, because of the remaining contaminants therein, which must either be removed or rendered relatively harmless, before the aqueous ellluent can be discharged intma-river or other body of water. Attempts have beenv made to meet this problem by passing the eilluent throughfiltering systems of various types, but the solids andgreases. tend to clog up or accumulate in thesystemr' I a a The present invention contemplates, :broadly,

improvements in method and equipment for over,-

coming problems such as thoseabove referred to, and particularly for clarifying the 1 efiluent from centrifuges, notably by a novel and advantageous method and apparatus for effecting separation of the greases, colloids and, fine solids.

More specifically, these; purposes areaccom- .plished, according to the present invention, by a novel flotation and skimming method, carried out by improved equipmcnthereinafter disclosed.

Still mor specifically, this *methodinvolves a progressive concentration or accumulating -01 greases, ,fine solids, and colloids,- by ;flotation; progressive skimming, scraping or otherwise re;-

M l ud ssnsis 4 I moving thefloated sconcen'trated materials, par ticularly in a periodic or step-by-step manner;

and drawing offof theclarifiedaqueousliquid, I

particularly by subcanting;

Further; the invention" con templ ates such a method wherein-the progressiveremoval of the 'floated concentrated materials is done in a partial periodic manner, i. e. apart only of the floatin mass of accumulated or concentrated materials is removed at any one time, so that the remaining layer or layers act as acovering or seal over th'e surface of the aqueous liquid which appears to be of great importance in facilitating or promoting the continued separation oi the materials by flotation.

Specifically, according to the present preferred practice "of the'lnvention, the partial'periodic removal ofthe floated materials ls periormed once each day; to an amount substantially equaling one days accumulation, while maintaining on the surface of-the liquid at least one days, and

preferably two days, accumulation. 1 The-invention further involves the practice of the method hereinbefore describedin such manner that'for the greater part of each flotation'period (for instance, of each 24 hour periodfthe body of liquid withitsseal of fioating'materials is left in a Quiescent state. This is preferably accomplished by following'aperio'dic practicein the subcanting of theolaLrified liquid, from= the vessel or tank employed, and in the delivery to said tank of the fresh ellluent; and by'properly coordinating this practice with the skimming procedure. Thisis best done; according to the invention, by: (1) subcanting the clarified aqueous liquid (which has undergone undisturbed clarification by the flotation process for about 24 such as above described which includes also the aeration of the liquid prior to the flotation part of :the operation. 1 This is particularly advantageous inthe treatmentof' materials having a high content of greases/such as sewage centrifuge eilluent, and according tothe preferred practice this aerationstep is accomplished by ified liquid and to deliver liquid tobe.clarified;

the piping system being so constructed and arranged that a diffusion or bailiing of the. liquid,, particularly when entering the tank, is effected}. so as to prevent turbulent disturbance of the floating seal of concentrated greases and othermaterials.

How the foregoing objects and advantages are secured... together-with such others; as may ein cident. to; the invention, will appear-1 fromrt-he following: description, taken. together with the accompanying drawingfwhereim v V Figure 1 is. a. plan. view; ofthe preferred; form of equipment for; practicing. the. method of the invention; certain parts beingv in.- section onv the line |l of Figure 2;; and

Figure 2 is-a vertical'section taken on theline 2.--2 of Figure= 1,, with the contents. of.- the tank shown in. a. manner. toillustrate: a typical precitice of the method. of: the present invention.

It willbe observed: that the clarifier tank it has an; inlet manifold comprising-a: plurality of-horizzontal pipes 4 and a cross or interconnectingpipe 5- whiclrlatter is fed throu h a supply line Econtrolledsby valve Vi tiomwould be; the emuent-pipe, from a centrifuge handling sewage" sludge; The: pipes. 4? lie near the bottom; oi the; tank andjhave each a; pluralityof outlets 1" with outlet, bafiles; 8 located adjacent thereto, whereby: the; incnming liquid isfdifiused throughoutthe bottom; of the tank. without turbulence;

Although. the same manifold orpipe-system may by suitable; valvecontrol be utilized for subcanting'the clarified liquid, I. prefer to, employ a separate subcanting manifold, comprising two: series' of pipes'B; opening into the tank near the bottom thereof, which drain into a couple. of pipes, Ill, which latter are joined tor become a discharge conduit H controlledby valve V2.

Adjacent the top'of thetan-k is a: scraper mechanism comprising shafts l2, sprockets l3, fixed thereon, chains- Mzmounted on said sprockets, and scraper: blades 1-5 mountedon saidchains. Suitable guides (not shown) may beused tokeep the= scraper mechanism fromi'sagging; The direction ofrun of the chains is indicated by anarrow, and this scraper system may be turned in that direc} tionby handor by av suitable motor l-G.

Adjacent the: end ofthe' tank toward which the efi' ective pass of the scraper moves, I place a collection trough: ll, over the edge of which the scraper blades turn, and into; which they discharge the materials as scraped from the bodyof liquid in the tank. From the collection: imough, the accumulatedgreases, solids, etc; can be removed inan-ydesired manner; as by screw- Ha. for disposal in: any. preferred way.

The method, or process; of the, invention islbest understood. by; reference: to. Figure 2-,. wherein the strata ofmaterials. within; the tank 3; are illustrated-; The, major body; off the contents: or the tank indicated ata comprises acunrentcharge Pipe 6, in.a.typical installawhich has been delivered through the inlet manifold, for example one days delivery of efliuent from the centrifuge, and this body a is undergoing a separation, by flotation of the greases with entrained colloids and fine solids; all of these materials or contaminants gradually rising through the quiescent liquid, and leaving clarified liquid adjacent the, bottom. The. Progressive shading indicatestheprogressive flotationwhich is taking place.

The layer b represents (in the example being used for illustration) the preceding days floated and. concentrated materials,- which, in order to secure. the utmost results from the invention,

7 must-not be appreciably disturbed when scraping 011' one or. moresuperjacent layers.

The layer 0 represents the floated and concentrated. materials; of. the one-day period preceding that. oi layer b. According to a typical practice of'the invention, this layer'is ready to be scraped In. initiallystarting; operation of. the:- sys tem, for example in a sewage disposalv plant employing. centrifugesfor. removing; the-majon pro;-

vportion ofthe solids'from the'sludge,.a;days run of th centrifuge efiluent. would baled, intothe clarifier andallowed to-stand for about 24, hours. Subcanting of: the clarified liquid would then be eifected,, and the tank rcfilledwithv eiiiuent; from the? centrifuge, which would in, turn be permitted tostan'd quietfor, about 24 hours. Thereupon the clarified: liquid.:would, again be subcanted. and a new. charge of :eflluent delivered into; the tankhand the concentrated. or. amumulatedi greases and solids; oi. the first. .days flotation would. then be scraped oit orptherwise: removed, leaving; the.- sec.- ond daysflotation of materialsin place uponthe thirddays. massv of. liquidundergoingclarification.

With. the operationof they method thus. estabished, each. day thereafter the following steps would takecplacei onedays clarified liquidwould be: subcanted;v an. equivalent charge" of emuent would be: deliveredv to the. tank; one days. accumulation ofi floated materials would bescraped cit; and: the: tank would then remain: quiet for anothen24 hours (approximately).

From: the: foregoing itwill be evidentthat both the decanting and the; refilling. should besubject to; fairly close: control; particularly so: that the level of the top layer of floated materialscan. be

brought to: the.- properheightwith relation to the scraper mechanism; For this-Purpose the valves V I and: V! are provided; and the control of these isto: be. coordinated with the: operation of the scrapermechanism in; a mannerto: carry out the method-descrihedl In Figure 2; thedecanting andrrefilli'ng have just. been completed, and the refiil'ingahas. been. carried tosuch a pointthat-the floated layer 0- (of the second day'preceding). has

been brought up above the discharge. edgeaat. the lettend of the tank, ready-for removal: by-operation of th'escraper;

While-probably not essential in all fields, I find that aeration of the liquid to be clarified, for example by violent agitation. thereofi' j ust' before delivery to the tank (which aerationmay be accomplished by the action oi the centrifuge itself, orby supplemental or alternative means such as air jetsor mechanical agitating meansnot shown)", serves to speed up'the'flotationprocess and tore'nder it more thorough; i r

1h typical actual practice, where the centrifuge cflluent has contained anaverage of 3.12%" of the contaminatmgmaterials in question, and this has been subjected to the day-by-day process as above described, the average purity of the clarified water drawn off has been 99.64%; i."e.

it has had a remaining contaminants content of only 36%. V i

The advantages of this will be quite evident to those skilled in'the art, particularly in the field of sewage disposal; and it is thought that the manner in which the invention accomplishes the various objects and advantages set out at thebeginning of this specification will now be clear, without further elaboration. It is alsoobvious that various changes in timing of the cycle of the method, or in parts thereof, or in equipment employed, may be made within the spirit and scope of the invention as defined by the appended claims.

I claim:

1. The method of clarifying an aqueous liquid containing materials to be removed, which com prises separating such materials from the liquid by flotation in a manneryto form successive peri odio accumulations of the'materials on the-surface of the liquid, removing floated-materials at the top thereof while continuously maintaining at least one such periodic accumulation of said materials on the surface of the liquid, andwithdrawing clarified liquid and replacing it with fresh liquid to be clarified. g

2. The method of claim 1 wherein the removal of fioatedmaterialsis done in a periodic manner.

3. The method of clarifying an aqueous liquid containing materials to be removed, which comprises aerating the aqueous liquid and delivering it tation and maintaining thebody of liquid in said process comprisesadmitting a charge of such liqzone in a quiescent state during the flotation separation, and removing floated materials at stantially equal to'the accumulation of one 110- tation period.

5; A flotation process for clarifying aqueous liquids containing materials to be removed, which uid to a separating tank, maintaining a period of quiescence thereafter while forming at the surface by flotation a layer of material to be removed, withdrawing clarified liquid from a point below the level ofsaid layer, admitting a fresh charge of liquids to be clarified, and from floated material, leaving after each such removal time to time removing a portion only of the a layer ofmaterial covering the surface of the liquid undergoing clarification.

6. The process of claim 5 in which the liquids to be clarified are aerated prior to being admittedto thetank.: r

.- GEORGE E. HENKEL.

. 3 in a periodic manner to azonelof treatment,there separating such materials from the liquid by 110- 

